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Re: Some advice on inferring negated properties

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 16 Aug 2007 15:47:36 -0500
Message-Id: <p06230923c2ea669973d9@[]>
To: public-owl-dev@w3.org

>On Aug 16, 2007, at 8:28 PM, Swanson, Tim wrote:
>>Thanks again. I think you're right, the misunderstanding goes back to
>>talking at cross-purposes. I have just one more question.
>>>>(Admittedly, this is not the same thing as "directly" checking for
>>>>negative entailment, since it relies on the user's understanding of
>>>>semantics to make the jump from membership in the above class to the
>>>>negative entailment.)
>>>It's not a negative entailment (which for me means a *failure* to
>>>entail) but an entailment of a negation, but yes. For Matt's purpose
>>>this might be fine. OWL 1.1 statement entailment shall be added to
>>>Pellet in due course (esp to support SPARQL). One could, of course,
>>>write such a wrapper.
>>"negative entailment" = "failure to entail" (i.e. still unknown in the
>>open world)
>More typically known as "non-entailment" (e.g., non-subsumption as well).
>I've never specifically heard "negative entailment" before, so I see 
>I read it as a variant of "non-entailment".
>>"entailment of a negation" = "entailing that something is untrue" (i.e.
>>known to be false)
>Well, the *negation* is true (entailed), but of course the negated 
>sentence is false.
>>Is this the accepted language? (If so, I need to re-write some of our
>>in-house documents to comply with it.)
>I feel that the above is standard.

Right. Please, everyone: don't get not-entailed confused with entailed-not.

B is entailed by A when, if A is true then B has to be true.

The negation of B, not-B, is true when B is false, and vice versa.
So not-B is entailed by A when, if A is true then B has to be false.

This leaves open the further possibility (which is overwhelmingly 
more likely) that when A is true, nothing whatever follows about the 
truth or falsity of B. Then neither of B nor not-B are entailed by A.

(failure to entail B =/= B is unknown, since the first, but not the 
second, allows for the possibility that not-B is entailed. Unknown is 
failure to entail B and failure to entail not-B.)

love to all



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Received on Thursday, 16 August 2007 20:47:51 UTC

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